Field of the Invention
The present invention relates to nozzles for casting metal beams, such as H-beams and the like. The nozzle of the present invention allows a better control of the metal flow into a mould, yielding metal beams with low defects.
Description of the Related Art
In metal forming processes, metal melt is transferred from one metallurgical vessel to another, to a mould or to a tool. For example, as shown in FIG. 1 a ladle (11) is filled with metal melt out of a furnace and transferred to a tundish (10). The metal melt can then be cast through a pouring nozzle (1) from the tundish to a mould for forming slabs, billets, beams or ingots. Flow of metal melt out of a metallurgic vessel is driven by gravity through a nozzle system (1, 111) located at the bottom of said vessel. In particular, the tundish (10) is provided at its bottom floor (10a) with a nozzle (1) bringing in fluid communication the interior of the tundish with the mould. Some installations make without a tundish and connect the ladle directly to the mould.
In some cases, two nozzles are used for a single mould in order to ensure optimal filling of the mould and thermal profile of the metal flowing into the mould. This solution may be used for simple rectangular profiles, such as in U.S. Pat. No. 3,931,850, but it is usually used for moulding complex shaped metal parts, such as H-shaped beams or similar. For example, JPH09122855 discloses a H-beam mould fed by two nozzles located at the intersections between each flange with web of the H-beam (note that the “flanges” refer to the two lateral elements of the “H” and the “web” refers to the middle element connecting both flanges; H-beams are also often referred to as I-beams, the two terms being used herein as synonyms). Using two nozzles for a single mould yields several drawbacks. First, the production costs are increased since two nozzles are required, instead of a single one. Second, the flow rates of the two nozzles must be well coordinated during casting, lest the overall metal feeding flow becomes uneven. This is not easy to achieve.
H-beam casting installations have been proposed comprising a single nozzle per mould, thus solving the drawbacks discussed above associated with the use of two nozzles as described, for example; in JPS58224050, JPH115144, and JPH05146858. In each of the foregoing documents, a single nozzle comprising an end outlet as well as front ports opening at the peripheral wall of the nozzle is positioned at the intersection between one flange only and the web of the H-mould. Because of its offset position with respect to the mould such nozzles have a more complex front ports design which openings are not distributed around the perimeter of the nozzle symmetrically with respect to a vertical plane as it would be the case in nozzles positioned symmetrically with respect to a mould. They comprise at least a first front port extending parallel to the web, and opening towards the opposite flange of the H-mould. In order to ensure proper filling of the corners of the flange located on the nozzle side, the foregoing nozzles also comprise two front ports forming a Y with the first front port. The front ports usually extend downwards.
The size of the nozzle is limited by the clearance available at the intersection of the flange with the web of the H-mould, keeping in mind that contact between the nozzle and the mould walls should be avoided, lest solidified metal bridges would form between the nozzle and the cold mould walls. This has consequences on the flow rate achievable by such nozzles, which size of the peripheral wall is limited, thus limiting the size of the axial bore and front ports too. JPH09122855 proposes a pair of nozzles having a triangular cross-sectional shape, with rounded corners, in order to optimize the clearance available at the intersection points between each flange and the web of the H-mould. Said nozzles are provided with an end outlet only, also triangular in shape, and comprise no front ports.
The flow profile and thermal profile of the molten metal filling the mould are of course of prime importance to ensure the production of flawless beams. Both flow and thermal profiles in H-beam moulds are very sensitive to the design of such single nozzles and, in particular, to the number, location, and design of the front ports. For example, it is important to ensure a filling of the mould which is stable in time, that avoids as far as possible metal jets hitting a mould wall with excessive momentum, which creates uncontrolled turbulences and rapidly erodes the mould thus decreasing service life thereof. When vortices and turbulences are formed, cooling of the beam becomes more difficult to control and flaws appear.
It is an object of the present invention to provide a nozzle suitable for filling complex shaped moulds such as H-beams, T-beams, L-beams, C-beams, and the like, yielding enhanced control of the metal jets penetrating into such mould, resulting in smoother flow and thermal profiles and, ultimately, in metal beams with very low flaw concentrations. This and other advantages of the present invention are presented in the following sections.